1. Field of the Invention
This invention relates to inkjet printing systems and, more particularly, to a real time adaptive inkjet temperature regulation controller adapted to accurately control the temperature on an inkjet print head.
2. Description of the Related Art
Impact printing systems rely on permanently shaped character elements physically contacting a recording medium. An example of an impact printing system is a typewriter where the character elements are permanently shaped as individual letters of the alphabet. The individual character elements contact the paper through a print ribbon when actuated by a user. Impact printing systems are generally considered slow, bulky, and noisy. Impact printing systems are, therefore, not recommended for high speed printing applications.
Non-impact printing systems use a variety of techniques to cause a desired image to be formed on the recording medium without necessitating contact between an image element and the recording medium. Examples of non-impact printing systems include thermal and non-thermal inkjet printing systems. Thermal inkjet printing systems thermally stimulate tiny droplets of ink in a chamber causing the droplets to eject from each of a plurality of print head nozzles. The ejected drops of ink impinge on the recording medium at high speeds. The ejected drops of ink form selected images on selected locations of the recording medium.
A heating element is associated with each nozzle on the print head. The heating element might for example be a resistor located closely to the nozzle. The heating element is preheated with preheat data such that the ink in the chamber is maintained at a predetermined preheat temperature. When print data arrives, the heating element rapidly heats up from the predetermined preheat temperature to a firing temperature when a suitable current is applied to the heating element. A significant amount of thermal energy is transferred to the ink from the heating element resulting in vaporization of a small portion of the ink adjacent to the nozzle and producing a bubble in the chamber. The formation of this bubble, in turn, creates a pressure wave that propels a single ink droplet from the nozzle onto a nearby recording medium. By properly selecting the location of the ink heating mechanism with respect to the nozzle and with careful control of the energy transfer from the heating mechanism to the ink, the ink bubble will quickly collapse on or near the ink heating mechanism before any vapor escapes through the nozzle. If the preheat temperature is too high, the bubble vaporizes. If the preheat temperature is too low, the drop does not fire responsive to the print data.
Each image printed on the recording medium is made up of a plurality of ejected inkjet drops. The quality of the printed image depends on the size, placement, and timing of each inkjet drop. The size, placement, and timing of each inkjet drop, in turn, depend upon accurate temperature control of the corresponding ink chamber and heating element on the inkjet print head. Because the frequency of the nozzle firings is image dependent, it is difficult to predict the inkjet head temperature or to identify which portions of the inkjet head are at higher temperatures. Although slowing the head firing frequency lowers the inkjet head temperature, this is disadvantageous because it slows page throughput. It is therefore advantageous to control the temperature of the inkjet head in real time without necessarily slowing the head firing frequency. That is, it is advantageous to control the inkjet head temperature with as little delay as possible.
Additionally, market forces pressure manufacturers of inkjet printing systems to continuously improve image quality while reducing the cost of the overall printing system and improving printing speed. Thus, it is advantageous to accurately control the temperature of the inkjet head without incurring a cost burden to the product and consuming system performance.